Although mast cells play a critical role in allergic reactions, the cells are also involved in the protective immunity in the body. This study aims to investigate the role of mast cells in immune regulation during aberrant T helper (Th)2 responses. In this study, an adoptive antigen-specific Th2 response model was established with mast cell-deficient mice to test the role of mast cell in the immune regulation. Cell culture was employed to test the role of mast cells in the modulation of the expression of B cell lymphoma 6 protein (Bcl-6) in Th2 cells. The results showed that after adoptive transfer with immune cells, the mast cell-deficient mice showed stronger Th2 pattern responses in the intestine than that in the mast cell-sufficient mice. Mast cell-derived mouse mast cell protease-6 increased the expression of Bcl-6 in Th2 cells. Bcl-6 inhibited the expression of GATA-3 in Th2 cells, subsequently, forkhead box P3 was increased and the Th2 cytokines were reduced in the cells; the cells thus showed the immune regulatory properties similar to regulatory T cells. We conclude that bedsides initiating immune inflammation, mast cells also contribute to the immune regulation on Th2 polarization.